We propose to investigate the effect of prosthetic ankle motion on the mechanics of bilateral lower-limb amputee gait. Bilateral lower-limb amputees often walk with rigid or stiff legs, which may be due in part to insufficient compliance and ranges of motion in their prosthetic ankles. They may attempt to overcome prosthetic deficiencies with compensatory actions that increase their energy expenditure during gait. Most of the literature pertaining to amputee gait is concerned with persons having unilateral amputations, but it is difficult to identify areas where significant improvement is needed based upon data from unilateral amputee gait. Compared with unilateral amputees, persons with bilateral leg amputations have a greater need for improvement in prosthetic componentry because of their increased energy demand as they walk and their low speed of walking. Prosthetic performance during gait is easier to evaluate in bilateral amputees because they have fewer physiological control options available to them while they ambulate. Few outcome studies have been reported in the literature regarding their rehabilitation, and there have been no published quantitative gait studies on bilateral leg amputees to date. We will perform quantitative gait analyses in the VA Chicago Motion Analysis Research Laboratory on 30 bilateral transtibial (below-knee) and transfemoral (above-knee) amputees walking with and without prosthetic components that increase ankle motion. These components include the Endolite Multiflex Ankle to increase ankle dorsiflexion/plantarflexion and inversion/eversion, and the Otto Bock Ankle Torsion Adapter to increase transverse plane rotation. We hypothesize that increased ankle motion will significantly improve the gaits of bilateral lower-limb amputees. We will also study simulated bilateral amputee gait in 15 able- bodied persons by fitting them with orthoses that minimize knee and ankle motion. We hypothesize that able-bodied persons walking with constrained ankles and knees will have gait characteristics similar to bilateral amputees. The able-bodied walking pattern serves as a useful basis of comparison for different types of pathological gait, and we believe that altering the locomotor system of the able-bodied person can yield valuable information concerning the mechanisms of pathological gait. The results from this study will aid in identifying limitations in current prosthetic technology that inhibit normal patterns of walking in amputees.